Major alterations in transcription elongation and RNA processing occur between B cells and antibody secreting cells that drive production of protective immunoglobulins. ELL2, an important transcription elongation factor, acts with RNA polymerase II and pTEFb to overcome pausing at the Igh locus and enhance Ig secretion. Our conditional knockouts of ELL2 in mouse B cells showed altered mRNA processing of Igh, curtailed antigen-specific humoral responses, and reduction in: unfolded protein responses, ELL1 levels, plasma cell development, and long-term plasma cell formation. The other elongation factor family members, ELL3 and ELL1, have not been investigated during antibody secreting cell differentiation. This set of experiments will provide initial exploratory data on the potentially distinctive activities of these three ELL factors in B cell differentiation and may identify new players in antibody secreting cell differentiation. In Aim 1. We will determine the state of RNAP-II pausing examining the gene profiles of ELL2, ELL1, and ELL3 at the B cell stages by ChIP seq and ATAC-seq. We predict that ELL3 will occupy heavy and light chain enhancers, contribute to the expression of Bcl6, Pax5, and Spi1, and presage expression of blimp-1 and XBP-1 in B cells. In AIM 2. We will determine if ELL3 or ELL1 can substitute for ELL2 in driving B cells differentiation to antibody secretion by using ELL2 conditional knockout mice as recipients. These experiments will test the overall hypothesis that it is not only transcription bu also elongation that controls the transition from B cells to antibody production.